The pharmacokinetics of Terizidone (TZ) in comparison with cycloserine (CS) was compared. The trial proved that blood concentration of TZ was higher at all time intervals studied than the concentration reached in blood after the same doses of CS; yet this increase was not proportional to two molecules of CS contained in one molecule of TZ. The quantity of TZ excreted with urine was also higher, but the difference, as compared with the excreted CS, was not significant. The concentrations in the elderly patients were higher, and excretion was slower than in the younger ones. The high concentration of TZ in urine suggest the possibility of using this drug in treating genitourinary tuberculosis.